1. Field of the Invention
The present invention relates to a segment type liquid crystal display device which displays predetermined characters, figures and so on.
2. Description of the Prior Art
FIG. 1 is a plan view of a conventional segment type liquid crystal display device 1. In the liquid crystal display device 1, an area in which a segment side transparent electrode (a portion surround by a solid line) 2 and a common side transparent electrode (a portion surrounded by a broken line) 3 are opposing each other forms a display area 4 which is a multiple free choice shape. In the liquid crystal display device 1, as shown in FIG. 1, the area outside the display area 4 is a non-lighting area wherein, at least, one of the segment side transparent electrode 2 or the common side transparent electrode 3 does not present. As a result, an area wherein the voltage is applied between a pair of transparent electrodes (hereinafter referred to as an ON area) forms a black display (light interruption display) and an area wherein the voltage is not applied between a pair of transparent electrodes (hereinafter referred to as an OFF area) forms a white display (light transmission display), thus in a so-called positive display method, the black display is always formed in a white background color and the white display is not formed in a black background color.
Conversely, in a so-called, negative display method wherein the white display is formed in the ON area, and the black display is formed in the OFF area, the white display is formed always in the black background color and the black display can not be formed in the white background color.
In general, in the positive display, a visual angle range is narrow though a contrast ratio is high, and conversely, in the negative display, the contrast ratio is low though the visual angle range is wide, thus each display method has its own feature. Therefore, in the conventional liquid crystal display device, when the contrast ratio is to be raised in the white display in the black background color, or conversely, the visual angle range is to be widened in the black display in the white background color it was not possible to realize by the configuration of the ordinary liquid crystal display device.
Though a so-called double TN (twisted nematic) structure or a double STN (super twisted nematic) structure, wherein liquid crystal display elements are piled in two layers and one liquid crystal display element is used for negative-positive inversion, may be a means to solve the aforesaid problems, such problems as increase in manufacturing cost, weight and thickness of the liquid crystal display device are newly encountered.
As shown in FIG. 2, in the case of a multiple free choice shape display in which, for example, a white area 7 is in a black background color area 6, and furthermore, black characters, for example, "Characters and figures" are displayed therein, though it is, in principle, possible to solve the problem by providing, in the double TN structure, an electrode in one liquid crystal display element for negative-positive inversion, and mixing the negative display and positive display in the other liquid crystal display element, such problems as positioning accuracy of the liquid crystal display element and a discrepancy of displayed shape due to a parallax based on the thickness of the liquid crystal display element when looking obliquely may newly occur.
In the case of forming the display area in the liquid crystal display device, a segment electrode formed on the segment side transparent substrate and a common electrode formed on the common side transparent substrate are formed so as to be overlapped when the two transparent substrates are arranged oppositely. The overlapped portion forms a display area. Also, by forming a plurality of color filters of different colors on the liquid crystal layer side surface of either of a pair of transparent substrates constituting the liquid crystal display device, and forming, for example, the segment side transparent electrodes which correspond to each color filter in the display area, and moreover, respectively connecting the segment electrodes which are formed in response to the color filters of same color electrically, a color display can be realized.
FIG. 3 is an enlarged plan view of a segment side transparent substrate 11 in a conventional color liquid crystal display device. On the segment side transparent substrate 11, three kinds of color filters, for example, a red filter R, a green filter G and a blue filter B, formed into a fine rectangular shape are formed. In FIG. 3, in an area corresponding to the blue filter B, a first segment electrode 12 is formed and in an area corresponding to the red filter R, a second segment electrode 13 is formed. Accordingly, when the first segment electrode 12 is brought in an ON state (voltage applied state), the area corresponding to the blue filter B becomes the ON state, and when the second segment electrode 13 is brought in an ON state, the area corresponding to the red filter R becomes the ON state. Here, it is assumed that a common electrode is formed in the area including, at least, the first and second segment electrodes 12, 13.
In the liquid crystal display device using the segment side transparent substrate 11 shown in FIG. 3, by arranging a polarizing plate to form a cross polarization, a so-called normally white display, in which light is transmitted when the voltage is not applied, can be effected. Accordingly, in a non-voltage applied state, a white color is displayed as the background color in the liquid crystal display device. When the first segment electrode 12 is brought in the ON state, an orientation of liquid crystal molecules of a liquid crystal layer corresponding to the color filter B is changed to interrupt the light. As a result, a yellow color is displayed in the display area by mixture of the red and green colors. By bringing the second segment electrode 13 in the ON state, red light is interrupted and a cyan color is displayed in the display area by mixture of the green and blue colors. Furthermore, when both the first and second segment electrodes 12, 13 are brought in the ON state, the red and blue lights are interrupted and the green color is displayed in the display area. Thus, in the liquid crystal display device aforementioned, four kinds of colors, white, yellow, cyan and green, can be displayed.
In order to display any color among eight colors (white, cyan, magenta, yellow, blue, green, red and black) by combining the three colors, red, green and blue, first, second and third segment electrodes 14, 15, 16 must be formed for each of the three kinds of color filters R, G and B as shown in FIG. 4, and the first, second and third segment electrodes 14, 15, 16 must be driven separately, necessitating three signal lines for applying the voltage to each of the segment electrodes.
However, for wiring the three signal lines electrically independently as shown in FIG. 4, the width of a signal line 16a sequentially connecting the third segment electrode 16 must be made extremely thinner. This is not possible because a resistance value becomes extremely high in a wiring method using an ordinary transparent conductive film.
For example, in the general liquid crystal display device, the color filter is selected at 80 micron width and 300 micron length. Interval between respective color filters is 30 micron, and a surface resistance value of the transparent electrode (ITO: indium tin oxide) is selected at about 40 .quadrature./.OMEGA.. In this case, as shown in FIG. 4, when one transparent electrode is to be arranged at the interval of 30 micron, the width of transparent electrode becomes 10 micron, the interval between the transparent electrodes becomes 5 micron, the resistance value of the transparent electrode corresponding to 300 micron length of the single color filter becomes 40.OMEGA..times.300/10=1.2 k.OMEGA., and the resistance the several color filters becomes 10 to 30 times of 1.2 k.OMEGA.. Accordingly, it is hardly possible to drive electrically because of the high resistance value of the transparent electrode.
Likewise, in a manufacturing process of the liquid crystal display device, it is very difficult to pattern the transparent electrode of 10 micron wide on the transparent substrate of 30 cm to 45 cm square at the interval of 5 micron.
Accordingly, usually, the four kinds of color displays are effected by the electrode arrangement and wire connection as shown in FIG. 3. In this case, however, in the liquid crystal display device which is set, for example, in the normally white display, four colors of magenta, blue, red and black could not display. As such, in the conventional color liquid crystal display device, the kinds of display colors are restricted, and hence the display was not diverse.